In a method of obtaining an image by an electrophotographic printing method or an electrostatic charge developing method, an electrostatic charge image formed on a photoreceptor is developed with a toner charged by friction in advance and then fixed. In this process, the toner is required to firstly maintain a stable electric charge amount and to secondly exhibit fixability to the paper.
In addition, an apparatus to be used for obtaining an image by an electrophotographic printing method or an electrostatic charge developing method has a fixing section of a heating member, the temperature in the apparatus thus increases, and the toner is thus required not to block, namely, to exhibit storage stability.
Particularly in the fixing method using a heat roller, a decrease in temperature of the fixing section has been progressed from the viewpoint of energy saving, and the toner has been thus strongly required to exhibit low temperature fixability. In addition, a roller which is not coated with oil has been used as miniaturization of the apparatuses has been progressed, and the toner has been highly required to exhibit releasability from the heat roller, namely, non-offset property.
It is also required that dirt on the apparatus even at the time of continuous printing and fogging at the time of printing are not observed, that is, durability of the toner is required.
A binder resin for toner greatly affects the toner properties as described above, and a polystyrene resin, a styrene acrylic resin, a polyester resin, an epoxy resin, a polyamide resin, and the like are known. Recently, a polyester resin has particularly attracted attention since it exhibits excellent storage stability, low temperature fixability, non-offset property, durability, pulverizability at the time of manufacture of toner, and the like and exhibits performances in a favorable balance.
For example, Patent Literature 1 proposes a toner exhibiting excellent low temperature fixability, hot offset resistance, glossiness, durability, and storage stability:
Examples of the method for manufacturing a toner using a polyester resin may include a pulverization method and a chemical method. The pulverization method is a method of obtaining a toner by melting and kneading a polyester resin, a pigment (coloring agent), a releasing agent and the like, finely pulverizing the kneaded product thus obtained by using a pulverizer or the like, and classifying the pulverized product, and the pulverization method is industrially widely used. In recent years, a decrease in particle diameter of toner is desired in order to realize a high image quality of an image to be formed. In order to decrease the particle diameter of toner, the energy and time required for pulverization increase, the manufacturing process is complicated, and further the yield decreases in the pulverization method. Hence, a chemical method capable of more efficiently decreasing the particle diameter has increasing attracted attention.
Examples of the chemical method may include a method in which a material containing a polyester resin and other substances to be blended in the toner are dissolved or dispersed in an organic solvent capable of dissolving the polyester resin, the liquid is dispersed in an aqueous medium containing a dispersion stabilizer, granulation is conducted, the organic solvent is then removed from the resultant, the particles thus obtained are separated, washed, and dried to obtain toner particles; and a method in which a polyester resin is dissolved in an organic solvent, the liquid is emulsified in an aqueous medium containing a dispersion stabilizer if necessary, the organic solvent is removed from the emulsion to obtain a resin emulsion, other substances to be blended in the toner are finely dispersed in an aqueous medium, the dispersion is mixed with the resin emulsion, the fine particles are aggregated and thermally fused to obtain particles, the particles thus obtained are separated, washed, and dried to obtain toner particles.
In the case of a chemical toner manufacturing method using an organic solvent, process passability deteriorates, the thermal properties for each toner particle to be obtained and the amounts, mixing states, and the like of the substances to be blended in the toner are nonuniform, and troubles such as an harmful effect on the performance of toner are thus caused when a polyester resin exhibiting insufficient solvent solubility is used. Hence, it is important for the polyester resin not to have a solvent-insoluble matter derived from gel, a crystal component, and the like and to exhibit favorable solvent solubility.
On the other hand, in recent years, a carbon neutral strategy has particularly attracted attention from the viewpoint of environmental protection such as suppression of global warming, and it has been actively attempted to change plastics derived from conventional petroleum raw materials to plastics derived from vegetable raw materials with lower environmental impact. The use of components derived from vegetable raw materials in toner is also investigated.
For example, Patent Literature 2 proposes a toner using a binder resin for toner containing a raw material component derived from vegetables.